Optical zoom system for a light scanning electron microscope

ABSTRACT

For a confocal scanning electron microscope ( 1 ) an optical zoom system ( 41 ) with linear scanning is provided, which not only makes a zoom function possible, in that a variable magnification of an image is possible, but rather which additionally produces a pupil image in the illuminating beam path (IB) [BS] and thereby makes a variable imaging length possible (distance between the original pupil (En.P) [EP] and the imaged/reproduced pupil (Ex.P) [AP]) so that axially varying objective pupil positions can thereby be compensated.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a continuation of application Ser. No.10/967,318 filed Oct. 19, 2004, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates to an optical zoom system for a confocal scanningelectron microscope as well as to a confocal scanning electronmicroscope with such an optical zoom system.

Confocal scanning electron microscopes, which are normally constructedas laser scanning microscopes, are known in the state of the art, forexample, let us cite patent DE 197 02 753 A1 in reference thereto. Mostrecently, components and technical systems from microscopy, specificallyfrom confocal imaging laser scanning microscopes, have been ever morefrequently applied to spectroscopic imaging techniques. In this manner,it is possible to survey the spectroscopic characteristics of a selectedspecimen region without destroying or touching the probed area. Confocaloptic microscopy thereby makes it possible to selectively detect opticalsignals, which are generated within a confocal volume with limiteddiffraction whose magnitude lies in the realm of micrometers. Laserscanning microscopes with scanning laser beams and/or with probing feedunits can generate high focal resolution for two or three dimensionalrepresentations of the specimen under examination. Owing to thischaracteristic, confocal laser scanning microscopy has nearly asserteditself as the standard for fluorescent probes in the field of biomedicaltechnology.

Normally, laser scanning microscopes are used with interchangeableobjectives. Thereby, the problem frequently arises that it is only withgreat difficulty that constant pupil positions along the optical axiscan be achieved within a series of objectives. In some cases, axialdifferences of 40 mm can occur in the objective chamber, which can beshortened in the conjugate space of the scanning configuration betweenthe scan mirrors by up to 4 mm. Lateral straying of the illuminatingbeam cone from the pupil associated with such a mismatch of the pupil'sposition can lead to non-uniform illumination of the specimen duringscanning.

The object of the invention is therefore to create an opticalconfiguration for a confocal scanning electron microscope with which theproblems associated with the axially varying pupil position can beeliminated.

This task is resolved in accordance with the invention with an opticalzoom system for a confocal scanning electron microscope, which, in theilluminating beam path of the microscope, is connected in front of theobjective capturing the object, which produces an intermediate image ofthe object and images an entrance pupil of the illuminating beam pathwith variable magnification and/or with variable imaging length into anexit pupil.

The inventors recognized that the problems associated with the axiallyvarying position (in the direction of illumination) of the entrancepupil of the microscope objective could surprisingly be resolved by theappropriate design of the optical zoom system. Such an optical zoomsystem was indeed known in the state of the art, however, from entirelydifferent perspectives.

Laser scanning microscopes generate a specimen image in that anilluminating beam is guided over a specimen during scanning by means ofa scanning arrangement and by means of a detector arrangement, whichforms the image of the illuminated specimen region via the scanningarrangement by means of a confocal aperture, the irradiation originatingfrom the illuminated spot is absorbed. The diameter of the confocalaperture determines the depth resolution and the focal resolution. Theposition of the confocal aperture establishes the sectional planeposition in the specimen. The patent DE 196 54 211 A1 uses an opticalzoom system to adjust the effective diameter of the confocal aperture orfor the selection of the sectional plane position.

For laser scanning microscopes, the scanned image region can be selectedby the proper control of the scanner in its zoom function, but only inthe case of point to point scanning, in combination with a galvanometerscanner. In the case of parallel scanning, that is to say, scanning ofseveral points at the same time by laser scanning microscopes, zoomfunction cannot be achieved by a change in the setting of the scanningarrangement since, as a rule, the individually scanned points stand inan established geometric relation to one another that is alreadypredetermined by the configuration of the perforations in the disc, suchas, for example, in the Nipkow disc, or predetermined by the apertureplate geometry in the case of a multiple pinhole aperture configuration.

The U.S. Pat. No. 6,028,306 describes such a laser scanning microscopewhich realizes a source for multiple spot illumination by means of astationary confocal multiple pinhole aperture configuration, which isdesigned in the form of a plate with a multitude of perforations. Anoptical zooming unit is connected in front of the scanning arrangement,which makes it possible to magnify or scale down the multiple spotillumination. In this manner, a region of the specimen may be scannedbased on a selectable size.

Such an optical zoom system known for other applications in the state ofthe art is used in accordance with the invention now to variably controlthe imaging length (the distance between the entrance pupil and the exitpupil on the optical zoom system), whereby fluctuations in the axialpupil position of the entrance pupil of the microscope objective can beequilibrated. This approach is surprising for the very reason that saidconstruction known from the German patent DE 196 54 211 A1 does notcover the position of the pupil in the microscope as its subject matterand neither does the microscope in the U.S. Pat. No. 6,028,306. Theoptical zoom system in accordance with the invention therefore achievesa double function in that, on the one hand, the scanning fieldparameters can be adjusted by varying the magnification, and on theother hand, the transmission length can be adjusted in such a mannerthat an axially varying pupil position on the microscope's objective canbe compensated for.

The variable magnification attained by the optical zoom system alsomakes it possible to change the magnification setting of the scannedfield and does so specifically for multiple spot scanners operating inparallel, in which a zoom function based on intervention at the level ofthe scanning arrangement is not possible due to the fixed geometricinterrelation of the points projected in parallel over the specimen. Theknown approach of controlling spot to spot scanning in confocal scanningelectron microscopes in such a manner that an image field is scanned inthe desired and adjustable magnification is just as impossible in suchparallel scanning systems as it is in systems that operate withresonance scanners, that is to say, in rotating mirrors driven byresonance vibrations, since the maximum deflection available therecannot be adjusted.

A possible form of embodiment for parallel operating multiple spotscanners is represented, for example, by the known application of aNipkow disc, as revealed in the mentioned U.S. Pat. No. 6,028,306 or inWO 8807695 or also in the European patent EP 0 539 691 A1. Beyond that,the mentioned US patent specification depicts a laser scanningmicroscope that scans in parallel with a multiple pinhole aperture platewhich is preconnected to a corresponding microlens array such that amultiple point source is generated in the end effect. This process alsolends itself for a form of embodiment of the optical zoom system.Another conceivable approach for scanning a specimen by means ofparallel laser scanning microscopy, that is to say, for simultaneousscanning of multiple points, is presented by the use of a confocalslotted aperture.

The present zoom configuration is therefore particularly advantageousfor application in a confocal scanning electron microscope which isrealized with confocal multiple point imaging, in particular by means ofa Nipkow disc, of a confocal slotted aperture or of a multiple pointlight source.

An advantageous application of an optical zoom system in accordance withthe invention is furthermore provided by a confocal scanning electronmicroscope that exhibits a resonance scanner.

An objective achieves its maximum resolution in the case when theentrance pupil is fully illuminated. It is therefore purposeful toprovide the appropriate means to ensure that the optical zoom systemalways fully illuminates the entrance pupil of the objective, regardlessof the setting on the optical zoom system. As a consequence, anotherpurposeful embodiment of the invention provides for the arrangement ofan element acting as an aperture in the exit pupil of the optical zoomsystem, said element not being larger than the smallest exit pupil size,which occurs when the optical zoom system is in operation. As a resultof this, the size of the entrance pupil is independent from the selectedsetting on the optical zoom system. Said size is purposefully equal orsmaller than the size of the objective's entrance pupil.

During operation of the optical zoom system, the exit pupil can becomevery small when magnification is set to less than 1.0. If one wishes toavoid this very small exit pupil size as the lower value limit for thedesign, then it is purposeful to connect a telescope in front of theoptical zoom system which shall affect the corresponding pupil dilation.Purposefully, this telescope shall only be activated during beam sweepwhen the optical zoom system operates in the scaled down mode. In thiscontext, the concepts of “magnify” and “scale down” here relate to theimage of the specimen.

The activation of this telescope ensures that the exit pupil of thezoom, which is provided at a magnification of 1.0, can be established asthe lower limit for the design without causing the exit pupil to becomeso small during scaled down mode of the optical zoom system that theobjective's pupil might possibly become underfilled. Based in theinterchangeability of the objective, it is purposeful to design theelement operating as an aperture as being interchangeable if oneintentionally wishes to underfill the objective's pupil, that is to say,not to fully illuminate. In that case, for example, an adjustable irisdiaphragm or a mechanism with different interchangeable apertures wouldcome under consideration such as, for example, a focal wheel withdifferent pinhole apertures.

In an especially compactly built form of embodiment, the element actingas a lens aperture is realized by the scanning unit; for example, thelimited dilatation of the scanner mirrors can act as a lens aperture.

As previously mentioned, the optical zoom system in accordance with theinvention can adjust the length of the image in such a manner that anaxially varying pupil position of the entrance pupil of the objectivecan be equilibrated. It is therefore purposeful that the optical zoomsystem is controlled by a control unit to be adjustable in such a mannerthat in a first mode of operation, a variable image length is produced.In order to adapt the optical zoom system to an activated objective,such as to a pivoting objective, it is purposeful to maintainmagnification at a constant in this mode of operation.

Once the setting for the position of the pupil is in place, another modeof operation can be advantageously realized in which the magnificationis set by guidance of the control unit so as to implement a zoomfunction without varying the image length. By virtue of the action ofthe optical zoom system in this mode of operation, the scanned field canbe adjusted in terms of its size. If one synchronously uses acontrollable double axis scanning unit, then in addition to anddepending on the adjustment change in zoom magnification, a randomregion can be selected within the maximum permissible scanning field asa so-called “region of interest”, whereby this “region of interest” neednot be symmetrically located relative to the optical axis. Duringdetection beam sweep, this displacement factor as well as the zoommagnification in the direction of the detector are once more cleared sothat the observation of specific regions in a specimen is possible. Inaddition to this, images from different “regions of interest” can beacquired and subsequently recomposed into an especially highly resolvedimage.

An especially purposeful mode of construction of the optical zoom systemuses four optical groups to implement variable pupil imaging. For thesake of manufacturing, it is favorable to provide the four opticalgroups, as seen in the direction of illumination, with positiverefracting power, with negative refracting power as well as twice withpositive refracting power. Purposefully, at least three of the opticalgroups are individually and independently adjustable by means of drives,and the displacement occurs in such a manner that the focus frominfinite to infinite remains intact and depending on the mode ofoperation, the magnification or image length (pupil position) isadjusted. It can also be advantageous to design the last group, as seenin the direction of illumination, as one unit together with a scanningobjective that is standard to a confocal scanning electron microscope,said scanning objective being positioned in front of the scanner unit.Each group is preferably comprised of at least one lens. In order toachieve the best possible characteristics in terms of available spectralrange as well as possible apertures/field angles, the groups preferablyhave self-correcting capabilities in terms of image defects/imagingerrors.

The mentioned selection of a “region of interest” either exclusively byway of the zoom function realized by the zoom objective, or also inaddition to that, by way of an asymmetrical scanning mode of operationin the possible scanned field can further be improved by the use of anelement that rotates the beam path. If, for example, an Abbe König prismis inserted into the pupil of the illuminating beam path, then thescanned, zoomed scan field can be rotated. In the detection beam path(mode), this rotation is once again cleared by the prism. Such an AbbeKönig prism can be obtained, for example, from LINOS Photonics, Germanyand is known in the state of the art. For the mentioned design, it isrotatably arranged in the beam path, in proximity of the pupil since thebeam cones converge at their narrowest here, and therefore an especiallysmall prism can be used. Depending on the rotational angle, itintroduces a rotation around the double angle of the image field.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following, the invention shall be more closely detailed in anexemplary manner while referring to the drawing are shown in:

FIG. 1 a schematic representation of a laser scanning microscope withbeaming source module, scanning module as well as detector module,

FIG. 2 a schematic representation of the beam path between the opticalzoom system provided in the laser scanning microscope in FIG. 1 and thespecimen acquired with the laser scanning microscope,

FIG. 3 a curve for visualizing pupil diameters in the construction inaccordance with FIG. 2,

FIGS. 4 a, 4 b and 5 a, 5 b as well as 6 a, 6 b various settings on theoptical zoom system of FIG. 2, wherein the figures designated with bshow a sectional representation which is rotated by 90° as compared tothe figures designated by a,

FIG. 7 a diagram with the positioning of the four optical groups of theoptical zoom system in FIGS. 4 through 6 for a first mode of operationwith constant imaging length,

FIG. 8 a diagram with the setting of the four optical groups for asecond mode of operation with constant magnification,

FIG. 9 a representation similar to FIGS. 7 and 8, however for a mode ofoperation with synchronous variation in imaging length andmagnification,

FIG. 10 a schematic representation of a scanned field for visualizingpossible zooming effects,

FIG. 11 a schematic representation of a laser scanning microscope with aNipkow disc,

FIG. 12 a schematic representation of a laser scanning microscope withparallel multiple spot illumination and scanning.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically shows a laser scanning microscope 1, which isbasically comprised of five components: of a beaming source module 2,which generates excitation radiation for laser scanning microscopy, of ascanning module 3, which conditions the excitation radiation andproperly deflects it for scanning over a specimen, of a microscopemodule 4, only schematically shown for the sake of simplification, whichdirects the scanning beam made available by the scanning module in amicroscopic beam path over the specimen, as well as of a detector module5, which receives and detects optical irradiation from the specimen. Thedetector module 5 can hereby be spectrally designed to have multiplechannels, as represented in FIG. 1.

The beaming source module 2 generates illuminating radiation, which issuited for laser scanning microscopy, more specifically, radiation whichcan release fluorescence. Depending on the application, the beamingsource module exhibits several sources of radiation to this end. In arepresented form of embodiment, two lasers 6 and 7 are provided in thebeaming source module 2, after which are connected on the load side alight valve 8 as well as an attenuator 9 and which couple theirradiation into a fiber optical wave guide 11 via a coupling point 10.The light valve 8 acts as a beam deflector by which beam cut-out can beaffected without having to switch off the operation of the very lasersin the laser unit 6 or 7. The light valve 8 is designed as an AOTF whichdeflects the laser beam, before coupling into the fiber optical waveguide 11, in the direction of a light trap, not represented here, forthe purpose of cutting out the beam.

In the exemplary representation of FIG. 1, the laser unit 6 exhibitsthree lasers B, C, D, whereas laser unit 7 only comprises one laser A.The representation in FIGS. 6 and 7 is thus exemplary of a combinationof single and multiple wave length lasers which are individually or alsocollectively coupled to one or several fiber optics. Coupling can alsobe done simultaneously via several fiber optics whose radiation is mixedby a color combiner at a later point after running through an opticaladaptor. In this manner, it is possible to make use of the most variedwavelengths or wavelength ranges for excitation radiation.

The radiation coupled into the fiber optical wave guide 11 isconcentrated by means of optical collimation systems 12 and 13 slidingover beam uniting mirrors 14, 15 and is modified in terms of its beamprofile in a beam forming unit.

The collimators 12, 13 ensure that the radiation conducted from thebeaming source module 2 to the scanning module 3 is collimated into aninfinite beam path. In each case, this is advantageously achieved by asingle lens which, under the control of a (non represented) centralcontrol unit, has a focusing function by its displacement along theoptical axis in that the distance between the collimator 12, 13 and therespective end of the fiber optical wave guide is modifiable.

The beam forming unit, which shall later be explained in more detail,generates a column-shaped beam from the rotationally symmetrical,Gaussian profiled laser beam, as it exists emergent from the beamuniting mirrors 14, 15, said column-shaped beam no longer beingrotationally symmetrical in its profile but rather suited for generatingan illuminated rectangular field.

This illuminating beam, also referred to as column-shaped, serves asexcitation radiation and is guided to a scanner 18 via a primary colorsplitter 17 and via an optical zoom system, yet to be described. Theprimary color splitter shall also be detailed later, but let it just bementioned here, that it has the function of separating the excitationradiation from the irradiation returning from the specimen thatoriginated from the microscope module 4.

The scanner 18 deflects the column shaped beam into one or two axes,after which said beam passes through a scanning objective 19 as well asthrough a tube lens and an objective of the microscope module 4 to bebundled into a focus 22, which lies in a preparation or in a specimen.The optical image is hereby produced such that the specimen isilluminated in a focal line with excitation radiation.

Fluorescent radiation excited in the linear focus in such a mannerarrives, via the objective and the tube lens of the microscope module 4and via the scanning objective 19, back at the scanner 18 so that in theopposite direction after the scanner 18, a beam once more at rest is tobe found. One therefore also speaks of it in such terms that the scanner18 descans the fluorescent radiation.

The primary color splitter 17 lets the fluorescent radiation lying inwave length ranges other than those of the excitation radiation pass sothat it can be rerouted via the deflecting mirror 24 into the detectormodule 5 and then be analyzed. The detector module 5 exhibits in theform of embodiment in FIG. 1 several spectral channels, that is to say,the fluorescent radiation coming from the deflecting mirror 24 isdivided into two spectral channels in a secondary color splitter 25.

Each spectral channel comprises a slotted aperture 26 which produces aconfocal or partially confocal image of the specimen 23 and whoseaperture size establishes the depth of focus with which the fluorescentradiation can be detected. The geometry of the slotted aperture 26therefore determines the microsectional plane within the (thick)preparation from which fluorescent radiation is detected.

Arranged after the slotted aperture 26 is also a blocking filter 27,which blocks off undesirable excitation radiation arriving at thedetector module 5. The column-shaped fanned-out beam separated off insuch a manner, originating from a specific depth segment is thenanalyzed by an appropriate detector 28. The second spectral detectionchannel is also constructed in analogy to the depicted color channel,and also comprises a slotted aperture 26 a, a blocking filter 27 a aswell as a detector 28 a.

The use of a confocal slotted aperture in the detector module 5 is onlyexemplary. Of course, a point to point positioning scanner can also beproduced. The slotted apertures 26, 26 a are then replaced by pinholeapertures and the beam forming unit can be omitted. Incidentally, all ofthe optical components for such a construction are designed to berotationally symmetrical. Then also, instead of single spot scanning anddetection, basically random multiple point configurations can be usedsuch as point clusters or Nipkow disc concepts, as shall yet be detailedlater by way of FIGS. 11 and 12. However, it is then essential that thedetector 28 have positional resolution since parallel acquisition isaffected on several probing spots by the scanner during sweeping.

In FIG. 1 it can be seen that the Gaussian bundle of rays, occurringafter the movable, that is to say, sliding collimators 12 and 13, ismade to converge via stepped mirrors in the form of beam uniting mirrors14, 16 and with the construction shown, comprising a confocal slottedaperture, is then subsequently converted into a bundle of rays with arectangular beam cross profile. In the form of embodiment in FIG. 1, acylinder telescope 37 is used in the beam forming unit, after which isarranged an aspherical unit 38 followed by a cylindrical lens system 39.

After reshaping, a beam is obtained which, on a sectional plane,basically illuminates a rectangular field wherein the distribution ofintensity along the longitudinal axis of the field is not Gaussianshaped but rather box shaped.

The illumination configuration with the aspherical unit 38 cansimultaneously serve to fill the pupil between a tube lens and anobjective. By such means, the optical resolution of the objective can befully exploited. This variant is therefore equally purposeful in asingle spot or multiple spot scanning microscope system, e.g., in a linescanning system (in the case of the latter, in addition to the axis inwhich the focus is on or in the specimen).

The excitation radiation transformed into a line, for example, is guidedto the primary color splitter 17. Said splitter is designed in apreferred form of embodiment as a spectrally neutral splitter mirror inaccordance with the German patent DE 10257237 A1, the contents of whoserevelation are fully integrated here. The concept of “color splitter”also covers splitter systems acting in a non-spectral manner. In placeof the described spectrally independent color splitter, a homogeneousneutral splitter (e.g., 50/50, 70/30, 80/20 or such similar) or adichroic splitter can also be used. In order to make an applicationbased selection possible, the primary color splitter is preferably to beprovided with mechanics that make a simple change possible, for exampleby a corresponding splitter wheel which contains individual,interchangeable splitters.

A dichroic primary color splitter is especially advantageous in the casewhen coherent, that is to say, when oriented radiation is to be detectedsuch as, for example, Stoke's or anti-Stoke's Raman spectroscopy,coherent Raman processes of higher order, general parametric non-linearoptical processes such as second harmonic generation, third harmonicgeneration, sum frequency generation, two photon absorption and multiplephoton absorption or fluorescence. Several of these processes fromnon-linear optical spectroscopy require the use of two or of severallaser beams that are co-linearly superimposed. To this end, thedescribed unification of beams from several lasers proves to beespecially advantageous. Basically, the dichroic beam splitters widelyused in fluorescence microscopy can be applied. It is also advantageousfor Raman spectroscopy to use holographic notch splitters or filters infront of the detectors to suppress Rayleigh scattering.

In the form of embodiment in FIG. 1, the excitation radiation or theilluminating radiation is guided to the scanner 18 via a motor drivenoptical zoom system 41. With this setup, the zoom factor can be adjustedand the scanned visual field is continuously variable within a specificrange of adjustment. Especially advantageous is an optical zoom systemin which the position of the pupil is maintained throughout thecontinuous tuning process while the focal position and the imagedimensions are being adjusted. The three degrees of freedom of the motorfor the optical zoom system 41, represented in FIG. 1 and symbolized bythe arrows, exactly correspond to the number of degrees of freedomprovided for the adaptation of the three parameters, the imagedimensions, the focal position and pupil position. Especiallyadvantageous is an optical zoom system 41 with a pupil on whose exitface a stationary aperture 42 is arranged. In a simple and practicalembodiment, the aperture 42 can also be provided by the delimitation ofthe mirror surface of the scanner 18. The exit face aperture 42 with theoptical zoom system 41 achieves the following:

that independent of the adjustment made on zoom magnification, there isalways a fixed pupil diameter formed on the scanning objective 19.Thereby, the objective's pupil remains completely illuminated evenduring random selection on the optical zoom system 41. The use of anindependent aperture 42 advantageously prevents the incidence ofundesirable stray radiation in the range of the scanner 18.

The cylindrical telescope 37 works together with the optical zoom system41, said telescope also being activated by a motor and connected beforethe aspherical unit 38. It is selected in the form of embodimentpresented in FIG. 2 for reasons of compactness, but this need not be thecase.

If a zoom factor of less than 1.0 is desired, the cylindrical telescope37 is automatically pivoted into the optical path of the beam. Saidtelescope prevents the aperture diaphragm 42 from being incompletelyilluminated when the zoom objective 41 setting is scaled down. Thepivotable cylindrical telescope 37 thereby ensures that even with zoomfactor settings of less than 1, that is to say, independent of anyadjustment change in the optical zoom system 41, there will always be anilluminated line of constant length on the locus of the objective'spupil. As compared to a simple visual field zoom, losses in laserperformance as expressed in the laser's illuminating beam are avoidedowing to this.

Since an image brightness jump cannot be avoided in the illuminationline when the cylindrical telescope 37 is being pivoted, it is providedin the (non-represented) control unit, that the feed rate of the scanner18 or the gain factor for the detectors in the detector module 5 isadapted accordingly when the cylindrical telescope 37 is activated sothat the image brightness can be maintained at a constant.

In addition to the motor driven optical zoom system 41 as well as to themotor activated cylindrical telescope 37, there are also remotecontrolled adjusting elements provided in the detector module 5 of thelaser scanning microscope in FIG. 1. To compensate for longitudinalcolor errors, for example, are provided, before the slotted aperture, acircular lens 44 as well as a cylindrical lens system 39, and directlybefore the detector 28, a cylindrical lens system 39, all of which arerespectively motor driven to slide in the axial direction.

Additionally provided for the sake of compensation is a correcting unit40 which shall briefly be described in the following.

The slotted aperture 26 forms, together with a circular lens 44 arrangedin front of it as well as with the equally prearranged first cylindricallens system 39 as well as with the subsequently arranged secondcylindrical lens system, a pinhole objective of the detector assembly 5,wherein the pinhole here is realized by the slotted aperture 26. Inorder to avoid the unwanted detection of reflected excitation radiationin the system, there is yet a blocking filter 27 that is connected inadvance of the second cylindrical lens 39, which enjoys the properspectral characteristics to exclusively admit desirable fluorescentradiation to the detector 28, 28 a.

A change in the color splitter 25 or in the blocking filter 27unavoidably causes a certain tilt or wedge error during pivoting. Thecolor splitter can cause an error between the probed region and theslotted aperture 26; the blocking filter 27 can cause an error betweenthe slotted aperture 26 and the detector 28. To avoid the necessaryreadjustment of the position of the slotted aperture 26 or of thedetector 28, a plane parallel plate 40 is arranged between the circularlens 44 and the slotted aperture 26, that is to say, in the imaging beampath between the specimen and the detector 28, so that said plate can bebrought into various rocking positions by activation of a controller.The plane parallel plate 40 is adjustably mounted in a holding fixturesuited to this end.

FIG. 2 schematically shows a possible form of embodiment for the beampath in FIG. 1 between the primary color splitter 17 and a specimen 23arranged in the microscope module 4. The optical zoom system 41, whichis only depicted in FIG. 2 as comprised of two elements for the sake ofsimplification, effects in the illumination beam path IB [BS] a pupilimage. At the same time in the object beam path OB [GS], designated bythe dashed line in FIG. 2, an intermediate image II 1 [ZB1] is formed inthe optical zoom system 41. The optical zoom system focuses frominfinite to infinite. The exit pupil Ex.P [AP] of the optical zoomsystem 41 is purposefully circumscribed by the aperture 42, aspreviously mentioned, so that independent of any setting adjustments onzoom magnification, there is always a fixed pupil diameter on thesubsequently arranged scanning objective 19. In the microscope module 4,between the tube lens 20 and the objective 21, in the objective's pupilOP, is arranged an objective aperture OA [OB] which is filled by or evencompletely illuminated by the exit pupil Ex.P [AP]. Owing to this, themaximum objective resolution can be achieved.

FIG. 3 shows the effect of the aperture 42 for filling the objective'spupil OP [OP]. In reference to this in the diagram of FIG. 3, on thevertical axis, the pupil diameter d is entered and on the horizontalaxis, the magnification m [v] affected by the optical zoom system 41 isentered. Curve 60 shows the function according to which the pupildiameter would change without the aperture 42. The dashed line 61 showsthe pupil diameter with the aperture 42 in dependency on magnification m[v]. Finally, the dashed-dotted line 62 visualizes the course of thepupil diameter of the objective's pupil OP [OP]. As can be seen, byvirtue of the objective aperture OA [OB], which is smaller than theaperture 42, the objective's pupil is independent of magnification m[v]. Naturally, the objective aperture OA [OB] can also be designed withcorresponding versions in the objective 21; but it need not be aseparate component.

The FIGS. 4 a/4 b, 5 a/5 b as well as 6 a/6 b show different settingsfor the zoom objective 41, whereby said representation is inverted ascompared to that in FIG. 2, that is to say, the direction ofillumination runs from left to right in FIGS. 2 through 6. Furthermore,for the sake of simplification, the scanner 18 is not depicted in FIGS.4 through 6, nor in FIG. 2 as well. As can be seen in the exemplarymanner of construction represented in FIGS. 4 through 6, the zoomobjective is comprised of four optical groups G1 through G4, wherebygroup G1 has positive refracting power and is stationarily secured. Thesecond group G2 has negative refracting power and is moved together withgroups G3 and G4 which once more have positive refracting power. Themovement is affected in such a manner that focusing from infinite toinfinite is maintained and magnification or pupil position is set,depending on the mode of operation.

Furthermore, in an exemplary variant it is purposeful to design group G1with the scanning objective following as a unit; in this variant, thescanning objective is thus positioned before the scanner in thedirection of illumination (not shown in FIGS. 4 through 6).

Each group is comprised of at least one lens. To satisfy therequirements for the desired spectral ranges as well as for the targetedaperture/field angle, the groups are self-correcting, to the extentpossible, in terms of imaging errors.

FIGS. 7 through 9 schematically and exemplarily show the opticalmovement of the zoom lens systems in the groups G1 through G4, wherebythe focal distances are as follows: focal distance of G1, 45 mm; focaldistance of G2, 153 mm; focal distance of G3, 45 mm; focal distance ofG4, 89 mm. The focal distances are scaled to the transmission length L.

For the sake of visualization in FIGS. 4 through 6, the position of theexit pupil Ex.P [AP] is also drawn in as well as that of the entrancepupil En.P [EP]. The transmission length L is defined as the distancebetween the entrance pupil EnP [EP] and the exit pupil Ex.P [AP].Furthermore, in FIG. 4 a, the z-coordinate is entered, which is measuredalong the optical axis, for the four groups G1 through G4. The entrancepupil is hereby set to the 0 position.

The figures designated with “a” respectively show a sectional planewhich is rotated by 90° as compared to the figures designated with “b”.Thus, FIGS. 4 a, 5 a and 6 a contain the pupil beam path and FIGS. 4 b,5 b and 6 b the object beam path. Based on the confocal slotted apertureconfiguration with linear illumination used in the exemplary embodiment,a line is always present in the object beam path in those cases whenthere is a pupil in the pupil beam path, or in FIGS. 4 a, 5 a, 6 a, whenthere is a nodal point. In another type of confocal imaging (e.g., withNipkow disc, multiple spot scanner, single spot scanner) theinterrelations are different.

In FIGS. 5 a/5 b, a magnification factor of m [v]=1.4 is set, whereasthe setting in FIGS. 6 a/6 b affects a magnification of m [v]=2.0 at thesame imaging length. As compared to the imaging lengths in FIGS. 5 and6, the imaging length has been extended by 10 mm for the setting inFIGS. 4 a/4 b at the same magnification factor as in FIGS. 5 a/5 b. Theposition of the exit pupil Ex.P. [AP] drawn into the figures clearlyshows this.

The zoom objective 41 can therefore be operated in two different modesof operation. On the one hand, it is possible to change the setting formagnification m [v] while maintaining a constant imaging length L. Achange in the position drawn in FIGS. 5 a/5 b to the position inaccordance with FIGS. 6 a/6 b represents, for example, operation in thefirst mode of operation which produces a scanning field zoom. Thesettings possible for this in groups G2 through G4 can be seen in FIG.7, in which the coordinates of the groups G1 through G4 are enteredalong the z-axis, as represented in FIG. 4 a, as a function ofmagnification m [v].

The concept of “magnification” once more relates to the effect of theoptical zoom system, that is to say, to the magnification of the image.An image magnification is then attained when the optical zoom system hasindeed achieved a reduction of the image transmitted by the illuminationsource in the direction of illumination, that is to say, for example,when a focal line has been shortened. In contrast, in the directioncounter to illumination, that is to say, in the direction of detection,an enlargement takes place.

FIG. 8 shows a second mode of operation which changes the transmissionlength while maintaining constant magnification. Since the entry hasbeen made in millimeters along the z-axis, one can clearly see that thetransmission length can be varied, e.g., by up to 20 mm, when thesetting on the optical zoom system has been changed. The position of theexit pupil Ex.P. [AP] shifts from 180 to 200 mm in contrast to that ofthe entrance pupil (situated at 0 mm). The values in FIG. 8 relate to achange in the transmission length at a magnification factor of 1.0.

FIG. 9 shows a mode of operation which is comprised of a combination ofthe above-mentioned first mode of operation (FIG. 7) and of the secondmode of operation (FIG. 8). With the control of the optical groups G2through G4 (optical group G1 is once more not changed in its setting)shown in FIG. 9, the magnification m [v] is simultaneously varied withthe transmission length L (the latter results from the changed positionof the exit pupil in FIG. 9).

With the help of the optical zoom system 41 and within the maximumscanning field SF available, FIG. 10 shows how a region of interest(ROI) can be selected. If the control setting on the scanner 18 is leftsuch that the amplitude does not change, for example, as is forcibly thecase with resonance scanners, a magnification setting greater than 1.0on the optical zoom system has the effect of narrowing in the selectedregion of interest (ROI) centered around the optical axis of thescanning field SF. If the scanner is manipulated in such a manner thatit scans a field asymmetrically to the optical axis, that is to say, inthe resting position of the scanner mirrors, then one obtains an offsetdisplacement OF in the selected region of interest (ROI) in associationwith the zooming action. Based on the previously mentioned action of thescanner 18, namely of descanning, and based on a repeat run through theoptical zoom system 41, the selection of the region of interest (ROI) inthe detection beam path is again cleared in the direction of thedetector. One can hereby make a selection of the desired region ofinterest (ROI) within the range offered by the scanning image SF. Inaddition, for different selections within the region of interest (ROI),one can acquire images and then compose them into an image with highresolution.

If one not only wishes to shift the selected region of interest by theuse of an offset OF relative to the optical axis, but also wishes torotate said region, there is a purposeful form of embodiment whichprovides for an Abbe König prism in a pupil of the beam path between theprimary color splitter 17 and the specimen 23, which obviously leads tothe rotation of the image field. This image is also cleared in thedirection of the detector. Now one can measure images with differentoffset displacements OF and with different angles of rotation and afterthat, they can be computed into a high resolution image, for example, inaccordance with an algorithm, as described in the publication by M.Gustafsson, “Doubling the lateral resolution of wide-field fluorescencemicroscopy using structured illumination” in “Three-dimensional andmultidimensional microscopy: Image acquisition processing VII”,Proceedings of SPIE, Vol. 3919 (2000), p 141-150.

FIG. 11 shows another possible mode of construction for a laser scanningmicroscope 1, in which a Nipkow disc has been integrated. The lightsource module 2, which is highly simplified in its representation inFIG. 11, illuminates a Nipkow disc 64, via the primary color splitter 17in a mini-lens array 65, as described, for example, in the patents U.S.Pat. No. 6,028,306, WO 88 07695 or DE 2360197 A1. The pinholes of theNipkow disc illuminated via the mini-lens array 65 are imaged onto thespecimen located in the microscope module 4. In order to be able to alsovary the size of the image on the specimen side, an optical zoom system41 is again provided here.

As a modified arrangement of the mode of construction in FIG. 2, in theNipkow scanner, illumination is affected by passing through the primarycolor splitter 17 and the radiation to be detected is reflected out.Furthermore, as a modified arrangement of FIG. 2, the detector 28 is nowdesigned with regional resolving power so as to also properly enableparallel scanning of the multiple spots illuminated which is achieved bythe use of a Nipkow disc 46. Furthermore, between the Nipkow disc 64 andthe optical zoom system 41, is arranged an appropriate stationaryoptical lens system 63 with positive refracting power which transformsthe rays divergently exiting through the pinholes of the Nipkow disc 64into suitable ray bundle diameters. The primary color splitter 17 forthe Nipkow construction in FIG. 11 is a classic dichroic beam splitter,that is to say, it is not the aforementioned beam splitter with aslot-shaped or punctiform reflecting region.

The optical zoom system 41 corresponds to the mode of constructionpreviously detailed, whereby the scanner 18 now becomes redundant withthe Nipkow disc 64. Nevertheless, said scanner can be provided if onewishes to undertake the selection of a region of interest (ROI) detailedin FIG. 10. The same applies to the Abbe König prism.

An alternate approach with multiple spot scanning is shown in schematicrepresentation in FIG. 12, in which several light sources obliquely beaminto the scanner pupil. Here also, a zooming function can be realized bythe use of an optical zoom system 41 for imaging, to be configuredbetween the primary color splitter 17 and the scanner 18, as representedin FIG. 10. By simultaneous beaming of light bundles at different angleson a plane conjugate with the pupil, light spots are produced on a planeconjugate with the plane of the object, which are simultaneously guidedby the scanner 18 over subregions of the total object field. Data on theimages are generated by the evaluation of all subimages on a matrixdetector 28 with mapping resolving power.

As another form of embodiment coming under consideration is multiplespot scanning, as described in the U.S. Pat. No. 6,028,306, whoserevelation is fully integrated here in terms of this. Here as well, adetector 28 with positional resolving power is to be provided as inFIGS. 11 and 12. The specimen is then illuminated by a multiple pointlight source, which is realized by a beam expander with apost-positioned microlens array, which illuminates a multiple apertureplate in such a manner that a multiple point light source is produced.

The described invention represents a significant expansion of theapplication possibilities for high speed confocal laser scanningmicroscopes. The significance of such expanded development can bededuced from the standard literature on cell biology and from theprocesses described there on superfast cellular and subcellularprocesses¹ and from the applied methods of analysis with a multitude ofdyes².

See, for example:

¹B. Alberts et al. (2002): Molecular biology of the Cell; GarlandScience.

^(1,2)G. Karp (2002): Cell and Molecular Biology: Concepts andExperiments; Wiley Text Books.

^(1,2)R. Yuste et al. (200): Imaging neurons—a laboratory Manual; ColdSpring Harbor Laboratory Press, New York.

²R. P. Haugland (2003): Handbook of fluorescent Probes and researchProducts, 10^(th) Edition; Molecular Probes Inc. and Molecular ProbesEurope BV.

The invention has an especially great significance for the followingprocesses and developments:

Development of Organisms

The described invention is, among other things, suited for the analysisof developmental processes which are characterized foremost by dynamicprocesses ranging from tenths of seconds to hours in duration. Exemplaryapplications are described here, for example, at the level of cellgroups and whole organisms:

-   -   M. A. Abdul-Karim et al. describe in 2003 in Microvasc. Res.,        66: 113-125 a long term analysis of changes in the blood vessels        of living animals wherein fluorescent images were recorded at        intervals over several days. The 3D data records were evaluated        with adapted algorithms to schematically illustrate the        trajectories of movement.    -   D. R. Soll et al. describe in 2003 in Scientific World Journ.,        3: 827-841 a software based analysis of movement of microscopic        data on the nuclei and pseudopodia in living cells in all 3        spatial dimensions.    -   R. Grossmann et al. describe in 2002 in Glia, 37: 229-240 a 3D        analysis of the movements of microglia cells in rats, whereby        the data was recorded for up to 10 hours. At the same time,        after traumatic injuries, the neuroglia also react with rapid        reactions so that a high data rate and correspondingly large        volumes of data are generated.

This applies to the following points of emphasis in particular:

-   -   Analysis of living cells in a 3D environment whose neighboring        cells sensitively react to laser illumination and which must be        protected from the illumination of the 3D-ROI [regions of        interest];    -   Analysis of living cells in a 3D environment with markers, which        are subject to targeted 3D bleaching by laser illumination, e.g.        FRET experiments;    -   Analysis of living cells in a 3D environment with markers, which        are subject to targeted bleaching by laser illumination, and at        the same time, are also to be observed outside of the ROI, e.g.,        FRAP and FLIP experiments in 3D;    -   Targeted analysis of living cells in a 3D environment with        markers and pharmaceutical agents, which exhibit manipulation        related changes by laser illumination; e.g., activation of        transmitters in 3D;    -   Targeted analysis of living cells in a 3D environment with        markers, which exhibit manipulation related changes in color by        laser illumination; e.g., paGFP, Kaede;    -   Targeted analysis of living cells in a 3D environment with very        weak markers, which require e.g., an optimal balance in        confocality against detection sensitivity.    -   Living cells in a 3D tissue group with varying multiple markers,        e.g. CFP, GFP, YFP, Ds-red, Hc-red and such similar.    -   Living cells in a 3D tissue group with markers, which exhibit        function related changes in color, e.g., Ca+-marker.    -   Living cells in a 3D tissue group with markers, which exhibit        development related changes in color, e.g. transgenic animals        with GFP.    -   Living cells in a 3D tissue group with markers, which exhibit        manipulation related changes in color by laser illumination,        e.g., paGFP, Kaede    -   Living cells in a 3D tissue group with very weak markers, which        require a restriction in confocality in favor of detection        sensitivity.    -   The last mentioned item in combination with the one preceding        it.

Transport Processes in Cells

The described invention is excellent in its suitability for the analysisof intracellular transport processes since the truly small motilestructures involved here are to be represented, e.g. proteins with highspeeds (usually in the range of hundredths of seconds). In order tocapture the dynamics of complex transport processes, applications arealso often used such as FRAP with ROI bleaching. Examples for suchstudies are described here, for example:

-   -   F. Umenishi et al. describe in 2000 in Biophys. J., 78:        1024-1035 an analysis of the spatial motility of aquaporin in        GFP transfected culture cells. To this end, targeted spots were        locally bleached in the cell membranes and the diffusion of the        fluorescence was analyzed in the surroundings.    -   G. Gimpl et al. describe in 2002 in Prog. Brain Res., 139: 43-55        experiments with ROI bleaching and fluorescent imaging for the        analysis of mobility and distribution of GFP-marked oxytocin        receptors in fibroblasts. To realize this task, very high        demands are made on spatial positioning and resolution as well        as on the direct temporal sequence of bleaching and imaging.    -   Zhang et al. describe in 2001 in Neuron, 31: 261-275 live cell        imaging of GFP transfected nerve cells wherein the mobility of        granules was analyzed based on a combination of bleaching and        fluorescent imaging. To this end, the dynamics of the nerve        cells set very high requirements for the imaging speed.

Molecular Interactions

The described invention is particularly well suited for therepresentation of molecular and other subcellular interactions. To thisend, very small structures with high speeds (in the range of hundredthsof seconds) must be represented. In order to resolve the spatialposition necessary for the observation of molecular interactions,indirect techniques must also be applied such as, for example, FRET withROI bleaching. Exemplary applications are, for example, described here:

-   -   M. A. Petersen and M. E. Daily describe in 2004 in Glia, 46:        195-206 a two channel visual recording of live hippocampus        cultures in rats, whereby the two channels are spatially        recorded and plotted in 3D for the markers of lectin and sytox        over a longer period of time.    -   N. Yamamoto et al. describe in 2003 in Clin. Exp. Metastasis,        20: 633-638 a two color imaging of human fibrosarcoma cells,        whereby green and red fluorescent proteins (GFP and RFP) are        simultaneously observed in real time.    -   S. Bertera et al. describe in 2003 in Biotechniques, 35: 718-722        a multicolor imaging of        transgenic mice marked with timer reporter protein, which        changes its color from green into red after synthesis. The        recording of the image is affected as a rapid series of        3-dimensional images in the tissue of the live animal.

Transmission of Signals Between Cells

The described invention is excellent and very well suited for theanalysis of signal transmission processes that are usually extremelyrapid. These predominantly neurophysiological processes set the highestdemands on temporal resolution since the activities mediated by ionstranspire within the range of hundredths to smaller than thousandths ofseconds. Exemplary applications of analyses on the muscle and nervoussystems are described here, for example:

-   -   G. Brum et al. describe in 2000 in J. Physiol. 528: 419-433 the        localization of rapid Ca+ activities in muscle cells of the frog        after stimulation with caffeine as transmitter. The localization        and micrometer-precise resolution succeeded only by virtue of        the high speed confocal microscope used.    -   H. Schmidt et al. describe in 2003 in J Physiol. 551: 13-32 an        analysis of Ca+ ions in axons of transgenic mice. The study of        rapid Ca+ transients in mice with modified Ca+ binding proteins        could only be conducted with a high resolution confocal        microscope since both the localization of Ca+ activity within        the nerve cell and its exact temporal kinetics play an important        role.

1. An optical zoom system for use in a confocal light scanning electronmicroscope with linear scanning and having an illuminating beam path andan objective for capturing an object to be imaged, the illuminating beampath having an illuminating beam path entrance pupil, and the objectivehaving an objective entrance pupil, the optical zoom system beingadapted for positioning in the illuminating beam path in front of theobjective, the optical zoom system comprising: optical zoom entrance andexit pupils; means for adjusting the image magnification; means foradjusting the distance between the optical zoom entrance pupil and theoptical zoom exit pupil in such a manner that an axially varying pupilposition of the entrance pupil of the objective can be equilibrated; andmeans for maintaining the position of the objective entrance pupil whilethe means for adjusting the image magnification and the means foradjusting the imaging length are being adjusted, whereby the opticalzoom system produces an intermediate image of the object and images anentrance pupil of the illuminating beam path with at least one of avariable magnification and a variable imaging length into an exit pupil.2. The optical zoom system in accordance with claim 1, wherein theobjective has an entrance pupil, and the optical zoom system furthercomprises: setting means for selecting an optical zoom setting and sizemeans for affecting the size of the exit pupil independent from theselected setting of the optical zoom system, the size means acting as anaperture, the size of the exit pupil being smaller than the size of theobjective entrance pupil.
 3. The optical zoom system according to claim1, wherein the size means is selected from the group consisting of ascanner mirror, an iris diaphragm, and an aperture mechanism havingdifferent interchangeable pinhole apertures.
 4. The optical zoom systemaccording to claim 1, further comprising: control means for adjustablycontrolling the optical zoom system, for producing variablemagnification in a first mode of operation while maintaining a constantimage length, and for producing a variable image length in a second modeof operation while maintaining constant magnification.
 5. The opticalzoom system according to claim 1, further comprising: first, second,third, and fourth optical groups, wherein as seen in a direction counterto illumination, the first optical group has positive refracting power,the second optical group has negative refracting power, the thirdoptical group has positive refracting power, and the fourth opticalgroup has positive refracting power, and drive means for positioning atleast the second, third, and fourth optical groups.
 6. The opticalsystem according to claim 5, wherein each of the first, second, third,and fourth optical groups is self-correcting relative to imagedefects/imaging errors.
 7. A confocal scanning electron microscope,comprising: scanning means for guiding an illumination beam in the formof a line over an object to be imaged, an illuminating beam path havingan illuminating beam path entrance pupil, an objective for capturing theobject to be imaged, the objective having an objective entrance pupil,and an optical zoom system adapted positioned in the illuminating beampath in front of the objective and including: optical zoom entrance andexit pupils; means for adjusting the image magnification; means foradjusting the distance between the optical zoom entrance pupil and theoptical zoom exit pupil in such a manner that an axially varying pupilposition of the entrance pupil of the objective can be equilibrated; andmeans for maintaining the position of the pupil while the means foradjusting the image magnification and the means for adjusting theimaging length are being adjusted, whereby the optical zoom systemproduces an intermediate image of the object and images an entrancepupil of the illuminating beam path with at least one of a variablemagnification and a variable imaging length into an exit pupil.
 8. Theconfocal scanning electron microscope according to claim 7, furthercomprising a Nipkow disc providing confocal multiple spot imaging of oneof a confocal slotted aperture and a multiple point light source.
 9. Theconfocal scanning electron microscope according to claim 7, furthercomprising a resonance scanner.
 10. The confocal scanning electronmicroscope according to claim 7, further comprising an Abbe König prismlocated in the proximity of the exit pupil, the prism being rotatable inthe illuminating beam path.
 11. A method of analyzing developmentalprocesses, comprising the step of: analyzing dynamic processes rangingfrom tenths of seconds to hours at the level of cell groups and entireorganisms, using a confocal scanning electron microscope according toclaim
 7. 12. A method of analyzing intracellular transport processes,comprising the steps of: analyzing small motile structures with highspeed, using a confocal scanning electron microscope according to claim7.
 13. A method of analyzing molecular and other subcellularinteractions, comprising the steps of: analyzing very small structureswith high speed for the resolution of submolecular structures, using aconfocal scanning electron microscope according to claim
 7. 14. A methodfor studying fast signal transmission processes, comprising the step of:studying neurophysiological processes with high temporal resolution instudies in the muscle or nerve system, using a confocal scanningelectron microscope according to claim 7.